Horses show a considerable variation in their pattern of locomotion both within and between breeds. The three basic gaits in horses are walk, trot and gallop. The horses use these different gaits according to their speed, walk is used at slow speed, trot is a faster mode of locomotion and gallop is the gait horses normally use to run fast. However, some horses have the ability to also use alternative gaits, for example pace and toelt, and such horses are called gaited horses. A horse that pace moves the two legs on the same side in a lateral movement in contrast to a trotting horse that makes a diagonal movement where the diagonal front and hind legs move forward and backwards together. Furthermore, Icelandic horses are able to perform a fifth gait named toelt, which is a four beet gait with the same foot fall pattern as the walk. A characteristic feature of toelt is that the horse then always has at least one hoof touching the ground, giving a very smooth gait. Examples of other similar alternative gaits, also known as ambling gaits, are fox trot, the rack, running walk and paso cort. The alternative gaits vary in footfall pattern, timing, and cadence, and can be generally divided into four categories: pace, regular rhythm ambling, lateral ambling and diagonal ambling. Table 1 provides a classification of breeds as gaited or non-gaited horses. Most horse breeds are in fact non-gaited and only representative examples of such breeds are listed in the table. Horses representing breeds classified as non-gaited never or rarely are able to perform the alternative gaits whereas most or all horses from the gaited breeds can perform alternative gaits. There are more gaited breeds worldwide in addition to the ones listed in table 1. Sometimes, there is a considerable variation also within breeds as regards the pattern of locomotion. For instance, Icelandic horses are classified as four-gaited or five-gaited, where the former can perform walk, trot, gallop and toelt whereas the latter can also pace.
The Standardbred horse, used for harness racing has a unique ability to trot or pace at a very fast speed without falling into gallop which is the normal gait at high speed for a horse. In North America, a subpopulation of Standardbred horses that pace at very high speed has been developed. Other horse breeds used for harness racing includes breeds like the Cold-blooded trotter, Finnhorses, the Frensch trotter and the Orlove trotter.
The pattern of locomotion in horses is under strong selection in horse breeding. For instance, the ability to race using gallop, trot and pace are selected in Thoroughbred horses, Standardbred trotters and Standardbred pacers, respectively. Horses with the ability to use alternative gaits are also highly desired by some riders and is a trait upon which many specialized breeds have been developed. Methods for predicting the pattern of locomotion in a horse, i.e. its ability to use different gaits, would therefore have a great utility in the horse breeding industry.